Intended use - rafter.
Would be two joined boards be as strong as one of a larger size?
Minimum requirement is 140x45mm, maximum 190x70mm. I have timber 190x35mm. If I use two boards side by side, giving me 190x70mm, is this combination as strong as a single board 190x70mm or at least as one 140x45?

What are good ways to join such boards? Glue, nails, bolts, straps? Is there a technical term for this? I had difficulty searching for information, as most material found is for joining on a wrong side, ex making longer or wider boards, while I want thicker.

Size in mm is the actual size of dry finished timber.

  • You say not “making wider boards and you want thicker”. What’s the difference?
    – Lee Sam
    Jun 15 '20 at 7:09

good you're joining the wide sides togher to make a wider rafter, not joining the thin sides to make a taller one. joined they will be about as strong as the wider one. possibly even stronger, because the laminated beam will not have any flaws like knots that pass through the whole thickness.

"nail lamination" is a thing, it should be covered in your framing manual, but you can use screws or bolts if you really want to.


  • found "nail lamination" in our building code, now I know how to join these boards to the standard.
    – anm767
    Jun 15 '20 at 22:24

What you have sounds very much like what we Americans would call a 2" x 8" (nominal size, actual size: 1.5" x 7.5" - yeah, we're weird that way...).

What you're proposing is making a 4" x 8" (70x190mm) out of it by nailing the two pieces together. That's not only perfectly acceptable, it's very commonly done for use as a header over a door or window*. Usually, one puts columns (across the short dimension) of 2 or 3 framing nails (16d, ~0.131", 3.3mm) through the two boards every 6-8" (150-200mm) apart (along the long dimension).

Yes, this is very doable under US code and is very acceptable - it is probably acceptable under your local codes as well. You'd have to check your local building codes to confirm and to see if they have any specific requirements for nailing/screwing patterns and fastener sizes.

*For use as a header in a standard wall thickness, we also have to include a piece of 1/2" (12mm) thick plywood to make the header the same thickness as a standard 2x4" wall stud so that the finished surfaces are the same distance apart. This may or may not impact your situation.

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